In the late 1970s, Campbell coached football for Columbia University; today the 71-year-old coaches tech entrepreneurs through their knottiest problems. (Protégés include Google chairman Eric Schmidt and Twitter's founders.) He has big-company chops, having worked at Apple and Intuit, on whose boards he sits. Campbell doesn't advise so much as guide; he eschews attention, doesn't charge for his services, and rarely invests in the companies he helps. His independence -- and deep knowledge and connections -- makes him an ideal nonexecutive chairman.